The presently disclosed subject matter relates to an apparatus for determining the presence of inspiratory flow limitation which is known as a symptom of a sleep disorder, and the kind of the apnea/hypopnea condition based on the respiration of the subject.
As an apparatus of this kind, there is an apparatus in which a signal waveform corresponding to the respiratory condition of the subject is acquired overnight, and the presence of inspiratory flow limitation is visually determined from the shape of the signal waveform (for example, see U.S. Pat. No. 7,325,545).
As disclosed in Japanese Patent No. 4,588,461, a strip-like strain gauge is wound around the chest or the abdomen to detect a motion of the portion, and a result of the detection is collated with a signal waveform corresponding to the respiratory condition, to detect an apnea/hypopnea condition during sleep and to determine the kind thereof. Apnea/hypopnea conditions are roughly classified into two categories, namely, obstructive apnea/hypopnea in which a respiratory effort is continued in an airway obstruction condition, and central apnea/hypopnea in which a respiratory effort itself stops to cease the ventilation. The inspiratory flow limitation is used as an index indicating the obstructive apnea/hypopnea condition.
Attachments of various kinds of sensors for detecting an apnea/hypopnea condition during sleep to the body impose a large burden on the subject. On the other hand, the work of visually determining the presence of inspiratory flow limitation from an enormous number of measurement signal waveforms that were obtained from the respiration of the subject by an overnight measurement, and determining the kind of the apnea/hypopnea condition constitutes a very large burden on the person performing the diagnosis. In the case of a determination based on visual observations, it is difficult to eliminate differences in the determination due to the subjectivity and experience of the observer.